Strategic risk advisor 6 Alpha Associates has provided a Detailed UXO Risk Assessment for Network Rail as part of the five-year, multi-million pound redevelopment of London Bridge station.

London Bridge is a significant transport hub in central London and one of the busiest stations in Europe, serving more than 50 million passengers each year. As the oldest major station in the capital, it is currently being rebuilt as part of the £6.5bn Thameslink programme - with a brand new concourse and a redesigned platform layout that will allow a significant increase in services and connections.

Yet any major infrastructure project in the capital remains subject to a consistent background risk posed by unexploded ordnance (UXO). Over 18,000 tonnes of bombs were dropped on London during WWII, around 10% of which did not detonate on impact and now pose a significant UXO threat to the safe and timely completion of construction and civil engineering projects of this nature.

Should inadvertent detonation of an unexploded bomb occur, the consequences could range from blast and fragmentation damage to nearby buildings and the rupture and damage of underground services to severe equipment damage, and, in the worst-case scenario, critical injury or loss of life. Meanwhile, should UXO be discovered during construction works, project delays and disruption, combined with associated costs, could severely hamper the progress of a development.

It is therefore critical that the UXO risk on any site in central London is fully quantified and accounted for ahead of any construction work. As such, 6 Alpha Associates was engaged by Network Rail in May 2012 to provide a Detailed UXO Threat and Risk Assessment for the London Bridge redevelopment project.

Based on the initial historical data obtained from preliminary desktop studies, this detailed assessment, employing 6 Alpha’s unique database of all known UXO threats in the capital alongside a range of geo-referencing techniques, evaluated the likelihood of a contractor encountering UXO on site.

In doing so, it considered a range of factors including the likelihood of UXO having impacted the site, the possible range of ordnance, including their age, condition and sensitivity, the likely distribution of such threats across the site and the likelihood and potential consequences of initiating UXO as a result of the planned intrusive work.

On the basis of this study, 6 Alpha was able to recommend a range of suitable risk mitigation measures not only to ensure the safety of personnel on site but also to minimize the risks associated with project delay and disruption.

“UXO discovery and its initiation is a low probability, high impact event,” said Simon Cooke, Managing Director, 6 Alpha Associates. “While it’s rare that UXO severely impacts terrestrial construction projects, suitable measures must be taken in the early design phases to assess the risk of encountering a high explosive hazard on site and mitigating that risk.”

“In London, where a host of exciting infrastructure developments continues to shape the city, the UXO legacy is well-documented and it falls to project developers to act in a prudent fashion by seeking appropriate and timely risk management advice in the early design phases.”

“At London Bridge, guaranteeing site safety is the first step towards a successful, much-needed overhaul of the station and its services,” Cooke added.

With the first new platforms having opened early this year, the redevelopment of the station is set for completion in 2018.

Over the last ten years 6 Alpha Associates has provided UXO risk management support on thousands of construction and civil engineering projects worldwide, including Crossrail, Europe’s largest railway and infrastructure construction project. In 2009, the firm co-authored the CIRIA guidelines Unexploded ordnance: A guide for the construction industry which remains the best practice benchmark for managing UXO risks in the construction environment.